Lions cornerbacks Chris Greenwood, left, and Jonte Green work against each other during minicamp at their practice facility in Allen Park on June 10. / Jarrad Henderson/DFP

By Anthony Kuehn

Detroit Free Press Special Writer

Anthony Kuehn is editor of the Detroit Lions blog Lions Gab. His opinions do not necessarily reflect those of the Detroit Free Press nor its writers. Get in touch with Anthony at lionsgab@gmail.com or on Twitter @lionsgab.

Liability, weakness, undermanned and maligned. Those words were used to describe the Lionsí secondary leading up to the NFL draft, and with the release of Chris Houston, they have been dusted off and trotted out again. Local and national media have questioned general manager Martin Mayhewís decision to not address the secondary more heavily in free agency and the draft, especially if he was considering cutting Houston the whole time.

What are people using to determine that the Lionsí secondary is suspect? Iíve seen articles touting the 23rd-ranked pass defense, but that number is solely based on yards allowed. Last I checked, opponents didnít get points for eclipsing yardage totals. The Lions finished 19th in opponent passer rating and yards per attempt, but that doesnít provide much context. They finished 13th in the league for fewest passing touchdowns and 17th in interceptions, neither of which is great, but definitely not terrible.

I am not really sure where the supporting evidence is that proves the secondary was the Lionsí weakness last year. ProFootballFocus.com rated the Lions the 10th-best pass coverage team in the NFL last season. That factors in the linebackers as well, but the majority of the rating is based on the secondary. DeAndre Levy graded out as the third-best coverage outside linebacker, and Stephen Tulloch also graded as third best for inside linebackers. Thatís exceptional, but not enough to bolster the entire secondary.

Rashean Mathis graded out as the 23rd-best cornerback in the league, followed by Darius Slay at 68th, Bill Bentley at 80th and Chris Houston at 97th. The safeties fared better with Glover Quin and Louis Delmas 10th and 11th, respectively. So the safeties and linebackers helped the coverage rating, but how could the top-three cornerbacks grade so low and everybody else so high?

How are the coverage grades calculated? PFF takes the number of times a player is targeted and calculates a rating based on the outcomes of those targets. They track the number of passes caught, completion percentage against, yards, yards after the catch, longest reception surrendered, touchdowns surrendered, interceptions, passes defensed and QB percentage against.

Those grades are pretty heavily weighted on not allowing receivers to catch a lot of passes, but what was the Lionsí defensive strategy based on the past four years? Dropping seven men into zone and rushing the passer with four to force opponents to get rid of the ball quickly and not give up big plays. The Lionsí defensive strategy was willing to concede short completions and yardage to avoid giving up big plays and touchdowns.

The Lions ranked 13th in the league in passing touchdowns given up, which would indicate that they were achieving that goal. They did however, struggle with limiting the big plays as they were 27th in passing plays of over 40 yards and 17th in plays of over 20 yards. Why were the Lions a little more susceptible to the big plays, but stingy with touchdowns?

The Lionsí scheme regularly had the cornerbacks lined up 8-10 yards off the receiver and in zone coverage. The defense is designed to allow underneath completions and the secondary and linebackers rally to make the tackle for a short gain. Opposing offensive coordinators started attacking those tendencies by faking short routes and then going deep when the corners jumped the short route. Once the Lions started getting beat by double moves, the corners were in no manís land. They couldnít be aggressive defending the short routes because they had to be mindful of the double moves, and they couldnít just sit back and allow underneath completions all day. They had no choice but trust their reads and hope for the best, not a scheme conducive to success.

Now, to be clear, I am not saying the Lionsí secondary was a great unit last year or that they will be significantly improved this year. What I am saying is the performance suggests the secondary was limited in their effectiveness due to the scheme the Lions played. This yearís defensive scheme is going to be much different and more aggressive. Whether the Lions have the players to pull that off remains to be seen. For instance, James Ihedigbo replaces Delmas in the secondary, and he finished 72nd in coverage rating last year, which is obviously a big drop from Delmasí 11th.

Mayhewís actions this off-season seem to back up my belief that the scheme was limiting the Lions rather than the players. When you look at it through the proper context, it makes it much easier to see why the Lions havenít panicked about the secondary as much as the fans and many members of the media. Whether he is right or not wonít be determined until the season starts, but at least you can understand his point of view when you have some context.